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Pressure gain combustion (PGC) is widely considered to improve gas turbine thermal efficiency substantially. However, there is no consensus on the modelling in gas turbine performance simulation. Even though it remains the main tool for design studies, the steady-state 0D representation has difficulties in modelling the inherently intermittent behaviour of pressure gain combustion. Selecting the optimal gas turbine design is therefore difficult as common PGC models tend to underor overestimate performance. In this paper, an algebraic combustor model is inferred from published CFD data and varied to have an optimistic and pessimistic representation. These models among others will be used in an optimisation to identify the best gas turbine design with respect to thermal efficiency. The consideration of the secondary air system and blade metal temperatures ensure a realistic case study. At the end of this paper, sensitivity studies shed light on cycle design at uncertain combustor performance. The selected PGC models achieve an improvement in thermal efficiency between 3.8 – 6.6 percentage points compared to conventional isobaric combustion. However, this is less than half the 13.3 percentage points gain promised by ideal isochoric combustion. INTRODUCTION Pressure gain combustion is a technology that has the potential to substantially improve thermal efficiency for gas turbines. The benefit of isochoric combustion is associated with the reduced production of entropy during the combustion process compared to conventional constant pressure combustion. Though, this comes with a substantial drawback, namely an intermittent process which increases complexity. This is not only true for associated physics of PGC but also for modelling PGC in conventional steady-state gas turbine performance simulations. The principal question is what representative pressure at the combustor outlet should be used to describe this inherently unsteady process. Without a profound estimate no accurate cycle design is possible. In the past a gas turbine with PGC is approximated by the Humphrey cycle, the Zeldovich, von Neumann, Döring (ZND) cycle (Heiser & Pratt, 2002) and the Fickett-Jacobs (FJ) cycle (Vutthivithayarak, et al., 2012). Apart from assuming isentropic component behaviour, the assumption of idealistic isochoric (Humphrey) or detonative combustion given by the Chapman-Jouguet condition (ZND and FJ) overestimates overall performance. This is because neither model correctly captures the non-uniformity of the exhaust flow (Paxson, 2010) (Paxson & Kaemming, 2014). According to the same authors, PGC converts the usual Brayton / Joule cycle to something approaching an Atkinson cycle. Therefore, constant volume combustion is just the ideal case realisations such as pulsed detonation combustion or shockless explosion combustion aim to achieve. More realistic models of PGC were presented by (Nalim, 2002), (Endo, et al., 2004), (Paxson, 2004), (Goldmeer, et al., 2008). All of them are suitable for steady-state 0D gas turbine performance simulation. Therein, it is already assumed that the total kinetic energy at combustor exit during exhaust phase is not

A Comparison of Steady-State Models for Pressure Gain Combustion in Gas Turbine Performance Simulation